1. Field of the Invention
The present invention relates to a disc unit which drives a motor to rotate a disc used as a recording medium, and records information on the rotating disc and reads out recorded information therefrom.
2. Description of the Prior Art
As a typical disc unit, a floppy disc drive unit (referred to as FDD hereinafter) is known. The FDD records information on a magnetic disc assembly having a flexible disc shaped recording medium, a so-called "floppy disc," and reads recorded information therefrom. The FDD is structured to allow the insertion and ejection of the magnetic disc, to rotate the magnetic disc by means of a motor and to record and read out information by slidingly contacting a magnetic head on the magnetic disc. A typical FDD includes a base or a chassis for supporting constituent members. On the base or chassis are a disc insertion and ejection mechanism used for the insertion and ejection of the magnetic disc, a disc drive mechanism for driving a motor to rotate the magnetic disc, a head seek mechanism for moving a magnetic head to an arbitrary position in a radial direction of the magnetic disc, and a head load mechanism for loading and unloading the magnetic head on the disc. Further, the FDD is provided with a main control circuit board having a control circuit for controlling the overall FDD, a motor control circuit board having a drive control circuit used for the disc drive motor, a connector for interface to a host apparatus, and a connector for a power source or the like.
The FDD as described above is used as an external recording device for a host electronic apparatus such as a personal computer, a word processor or the like. The FDD can be structured as an independent single device, but in most cases it is structured to be incorporated in the main body of a host electronic apparatus. In recent years, progress has been made in making the electronic apparatus incorporating the FDD miniature and portable. In line with such progress, there are strong needs for miniaturization, thinning, and weight reduction of the FDD as well.
Conventionally, the FDD has a base body which is made by die-casting and has a complicated cross section. In contrast, one can consider making the base body from sheeting to provide an FDD which is thin, light, miniature and less expensive, with the cross section of the base body being of simple form, for example, U-shaped in the direction of width thereof.
One can also consider employing a thin shield cover for shielding noises, and using a light weight material which is comparatively inferior in strength, such as aluminum.
However, in the case of the base body as described above, sufficient mechanical strength cannot be obtained. Specifically, when an FDD having such base body is incorporated and mounted in the host electronic apparatus, there is a possibility of a strain therein which is caused by stress. The strain in the base body causes displacement of the constituent members of the FDD. A problem associated with this is that recording or reading out is not performed accurately and excellently, so that reliability suffers.
To eliminate the problem as described above, one might consider using a thick shield cover made from a material such as an iron plate having relatively large strength for mounting the base body for reinforcement. However, it is impossible to make the FDD miniaturized, thin and light in weight in this manner.
In the meantime, naturally, there is a further need for cost reduction which might be realized by reducing the number of components of the FDD, other than the FDD of a miniaturized, thin and light weight type. In the case of the conventional FDD, there is room for improvements including reduction in the number of components of the FDD, because it uses three screws for mounting a main control circuit board on the base body.
By the way, a rotating driving portion for rotating a disc includes a disc drive motor and a chucking mechanism for holding the disc and for transmitting to the disc a rotational driving force from the disc drive motor. In the conventional FDD, a spindle which is an output rotation shaft of a motor such as a direct drive motor (referred to as a DD motor hereinafter) has a top end to which a disc shaped spindle hub is secured. The chucking mechanism is provided in the spindle hub basing on the hub. Recording or reading out is performed in such a manner that while holding the disc on the spindle hub, the DD motor is driven to rotate the disc, and a magnetic head is brought into contact with the disc.
However, as described above, it would be desirable to make the conventional FDD thinner and miniaturized since it may be incorporated into a portable personal computer or a word processor. Since the conventional FDD has a DD motor provided with the spindle hub on its top end and the chucking mechanism is provided on the hub, it is hard to reduce the height of the whole rotating driving portion consisting of the DD motor and the chucking mechanism, which form the main portion of the FDD. This is an obstacle to making the whole FDD thin.
Further, when a belt driving system is applied to the rotating driving portion for rotating the disc, a pulley must be mounted in the rotating driving portion for receiving the motor driving force through a belt. This causes a difficulty in miniaturizing and thinning the rotating driving portion.
Additionally, to reduce electric power consumption, a DD motor having a pair of rotors can be employed when the direct driving system is applied to the driving portion for rotating the disc. It is desired that the rotating driving portion be miniaturized and made thin in this case also.